In cryogenic applications it has been found that commonly available cup or lip ring seals even when spring loaded suffer from leakage at low pressures because the sealing force provided by the spring is often used up by the cold flow of the seal. Cold flow is peculiar to fluorocarbons in that when the material is compressed over a prolonged period of time, it will flow in some available space losing some of its spring-force obtained during compression. Also, in the commonly available ring seals the outer diameter lip is in tension while the inner is in compression and this results in a waviness of the inner lip which the low working pressure is unable to correct.
While improvements in ring seal assemblies having a wedge member to spread the lips of a cup seal to assure a continuous fluid-tight contract has been recognized as shown in British Pat. No. 757,225 to George Osloff et al and U.S. Pat. No. 4,160,551 to J. D. Nixon, et al, the cooperating wedge member and cup were not of a construction which could be handled before installation in a unitary manner but of separate parts which needed to be assembled in place.